Medical practitioners insert intravenous (IV) catheters through a patient's skin to provide access for medications, fluids, and blood drawing. Insertion of an IV catheter can cause pain, which can reduce the level of cooperation by the patient, and can cause anxiety and other negative effects on the physical and mental well-being of the patient. The problems are particularly acute when the patient is a child.
To prepare the patient's skin for inserting a catheter, a practitioner cleans the skin and then anesthetizes it to reduce the pain. A topical anesthetic with 40% lidocaine has been used, but its use has been inconsistent because of concerns about irritation to the skin, systemic toxicity, and inadequate analgesia. Lidocaine-based anesthetics have also been injected, but this method of anesthetizing requires a needle stick. Attempts have been made, therefore, to produce a more desirable local anesthetic for IV insertions.
A promising topical anesthetic is sold under the name EMLA.RTM. (a registered trademark, and an acronym for "eutectic mixture of local anesthetics"). This anesthetic, which is typically applied as a cream, produces anesthesia equivalent to that achieved with a lidocaine injection, but without the needle stick. Even though EMLA anesthetic has been approved by the FDA, it is used to varying degrees because of difficulties in its application and use, and resulting non-compliance by patients.
To apply this anesthetic, a practitioner applies about 1-2 grams of cream per 10 cm.sup.2 of skin and leaves it on the skin for about an hour. An adhesive dressing, such as a TEGADERM.RTM. dressing (a registered trademark of 3M, located in St. Paul, Minn.), is often used to cover the cream and to keep it in contact with the skin. This dressing can be difficult to apply, however, and has some documented risks. The dressing has an adhesive that has a tendency to stick to itself, making it difficult to apply to skin surfaces. Moreover, it can lose its adhesion if the adhesive comes into contact with the cream. Secondary dressings, such as household plastic wrap and gauze, have been used to compensate for these problems.
Several other problems, particularly involving children, have been reported when applying the anesthetic in this manner. Children have rubbed the cream into their eyes when an inadequate covering has been applied to the hands, have ingested the cream and therefore caused upper airway anesthesia, and have chewed on the dressing.
Another way to apply this anesthetic has been with a patch impregnated with the anesthetic. To apply the patch, a seal is peeled away, so that the anesthetic can contact the patient's skin, and so that a stiff foam tape around the anesthetic holds the patch on the patient. This tape can become loose with flexion and movement, however, causing it to lose its adhesion, and thereby raising the risks to children as noted above. Patients may also have sensitivity to the tape on the patch and to its painful removal.
It is therefore an object of the present invention to improve the application of a topical anesthetic for injections, while reducing the drawbacks and risks that have been associated with the application of anesthetics.